Streaming audio from a Node.js server to HTML5 <audio> tag
Here's a (slightly outdated) summary of the current status of HTML5 Audio and Icecast streams.
As you can see, a MP3 source only seems to work in Safari (and possibly IE9). You might need to experiment with some server-side transcoding (with ffmpeg or mencoder) to OGG Vorbis. I'm pretty sure I was able to get Chrome to behave properly when I was sending Vorbis data.
Firefox was still being a brat though, maybe it doesn't like the chunked encoding (all SHOUTcast servers respond with a HTTP/1.0 version response, which hadn't defined Transfer-Encoding: chunked yet). Try sending a Transfer-Encoding: identity response header with the OGG stream to disable chunked, and Firefox MIGHT work. I haven't tested this.
Let me know how it goes! Cheers!